In the microelectronics industry as well as in other industries involving construction of microscopic structures (e.g. micromachines, magnetoresistive heads, etc.), there is a continued desire to reduce the size of structural features. In the microelectronics industry, the desire is to reduce the size of microelectronic devices and/or to provide greater amount of circuitry for a given chip size.
Effective lithographic techniques are essential to achieving reduction of feature sizes. Lithography impacts the manufacture of microscopic structures not only in terms of directly imaging patterns on the desired substrate, but also in terms of making masks typically used in such imaging. Typical lithographic processes involve formation of a patterned resist layer by patternwise exposing the radiation-sensitive resist to an imaging radiation. The image is subsequently developed by contacting the exposed resist layer with a material (typically an aqueous alkaline developer) to selectively remove portions of the resist layer to reveal the desired pattern. The pattern is subsequently transferred to an underlying material by etching the material in openings of the patterned resist layer or by ion implantation into the substrate at the spaces in the pattern corresponding to the removed portions. After the transfer is complete, the remaining resist layer is then typically removed.
For many lithographic imaging processes, the resolution of the resist image may be limited by anomalous effects associated with refractive index mismatch and undesired reflections of imaging radiation. High reflectivity from the substrate has become increasingly detrimental to the lithographic performance of photoresists for high NA and short UV wavelength (248 nm and 193 nm) exposures leading to undesirably high critical dimension (CD) variation on the wafer. This problem is even more pronounced in implant levels owing to the existance of topography (post gate level) and various reflective substrates (such as Si and SiO2 in pregate levels). Top antireflective coatings (TARC) have been used earlier, but their reflectivity control is not as good as bottom antireflective coatings (BARC).
Using conventional BARC requires an etch step (e.g., reactive ion etching) to remove the BARC. There is a concern that such etch processes could damage the substrate. Thus, the use of conventional BARC in the lithography step is not desirable for many applications including implant levels.
Developable BARC (DBARC) has been proposed to solve the damage issues associated with conventional BARC removal.
U.S. Pat. No. 6,844,131 describes a positive-working photoimageable bottom antireflective coating. This patent teaches the use of a polymer containing an acid labile group in combination with an absorbing chromophore. US Published Patent Application 20070243484 discloses a wet developable bottom antireflective coating composition and method for use thereof. This application teaches the use of a polymer containing no acid labile group. Both patent publications require the casting solvents for their DBARCs be different from the resist solvents. In most cases, these DBARC compositions require ketones and lactones. Ketones and lactones are usually either not safe enough or not good for spin-coating (the method commonly used to form layers of photoresist materials and BARCs on semiconductor wafers).
Therefore, there is a need for improved DBARC compositions that are especially suitable for use in 193 nm lithographic processes to be followed by ion implantation which DBARCs use solvents that are more compatible with conventional photoresist processing and application techniques (e.g., propylene glycol methyl ether acetate or PGMEA).